Some soil tests you can do are explained in a free (PDF document C221-DIY-Soil-Tests ) from Washington State University Extension.
In order to determine how good your soil is, you can try a simple observation test. First, understand this:
The soil is alive. In just one teaspoon of agricultural soil there can be one hundred million to one billion bacteria, six to nine feet of fungal strands put end to end, several thousand flagellates and amoeba, one to several hundred ciliates, hundreds of nematodes, up to one hundred tiny soil insects, and even earthworms. These organisms are essential for healthy growth of your plants. … A thriving population of diverse fungi, bacteria, insects, and invertebrates is one of the most visible signs of soil quality. The more that creeps and crawls under your garden, the less opportunity there is for pests and disease. Each level of soil life does its part to break down plant residue and make more nutrients available for plant growth. {WashExt}
To measure the animal life in your soil, digging down at least 6 inches and peer intently into the hole for 4 minutes. Contrary to the image for this article, you should be close to the soil to see well and the hole can be fairly small.
Count the number and species of each organism observed, such as centipedes, ground beetles, and spiders. Most soil organisms spurn daylight, so gently probe the soil to unearth the shyer ones. As a rule of thumb, if you count less than 10, your soil does not have enough active players in the food chain.
To find out why your soil organisms might be low, you could then consider the type of soil you have (too much clay? too much sand?) and also the pH which is how acidic or basic your soil is, the possible contaminants, and the soil nutrient profile.
The simple soil organism test is a great place to start when you want to grow some of your own food and need to know if your soil is going to provide healthy nutrients.
